Vibration control apparatus for a matrix printer



May 30, 1967 RIC. BURNS HETAL VIBRATION CONTROL APPARATUS FOR MATRIXPRINTER Filed Oct. 18, 1965 FIG.

mm W W ROBERT C. BURNS TATSUO HASEGAWA VICTOR R SIMPSON 8y 2% TTORNEY FIG.

United States Patent Ofiice 3,322,253 VIBRATION CGNTROL APPARATUS FUR AMATRIX PRHNTER Robert C. Burns, Conklin, Tatsuo Hasegawa, Endwell, andVictor R. Simpson, Owego, N.Y., assignors to international BusinessMachines Corporation, Arnionk, N.Y., a corporation of New York FiledOct. 18, 1965, Scr. No. 497,386 11 Claims. (Cl. 197-1) This inventionrelates generally to high speed printing apparatus and more particularlyto the construction of a vibration control apparatus for the printingelement in a serial matrix printer.

Printing machines are known in which the outlines of characters areformed by printing the appropriate dots of a bi-dimensional dot matrixhaving the same general size as the characters to be printed. Oneversion of such a machine, sometimes called a wire printer, employs amatrix of individually operable dot printing wire elements or the likewhich are projected in combination simultaneously toward a platen toeffect printing of the whole character on an interposed print medium.For printing a complete line of data, means are provided for effecting arelative longitudinal motion between the print matrix and the platen(and print medium) so that different charac ters are printed in seriesat successive positions along the print line.

In serial machines, the print head, having the wire matrix formedtherein, is moved along the print line while the print wires areactuated successively to record the characters composing the line ofprint. The print head may be moved incrementally or continuously alongthe print line and then, upon completion of the line returned to thestarting point for the next line, usually at the left side of the recordmember. The incremental motion is characteristically interrupted so thatone of the members moves in steps along the print line. It can beappreciated that if printing with incremental motion is to be performedat high rates of speed, the moving parts must be accelerated from rest,advanced, then brought to rest rapidly in short intervals of time. Inaddition, it is essential that the print head be returned to thestarting point for a new line immediately upon completion of a line witha minimum of elapsed time.

The attainment of fast operating speeds has, however, been severelylimited heretofore by excessive vibration and oscillating flexuralstresses created in the print tubes, especially during the retraction ofthe printing member from an extended position to its starting position.A further difliculty encountered was that the printing member wouldovertravel excessively during retraction and require additional timeadvancing up to the home position where printing could start on the newline. The construction of a satisfactory restraining device orarrangement by which vibration amplitude could be sufiicientlycontrolled was further complicated by the requirement that the initialstarting position for a print line be variable along the horizontal pathof movement traveled by the printing member. A construction which wasthus satisfactory for one starting position of the printing member wasineffective at another starting position. Since the initial or homeposition of the printing member varies, the rate at which lines areprinted also varies (for a given character rate) so that the amplitudeof vibrations either increased or decreased depending upon thecoincidence of the printing rate with the resonant frequency of theprinting member. Because of the variation in vibration amplitude, thenecessary incrementing force for the printing member applied at theprint head would also change thus creating 3,322,253 Patented May 30,1967 difficulty in keeping the increment time and distance carefullycontrolled.

Accordingly, it is an object of this invention to provide apparatus fora serial matrix printer which enables the printer to be operated atincreased speeds with improved print registration and control.

Another object of this invention is to provide apparatus for limitingvibration in a serial matrix print member.

A further object of this invention is to provide a flexible restrainingdevice for restricting objectionable vibrational and whiplash motionwhile yet permitting the necessary degree of movement for the printingmember in a serial matrix printer.

A still further object of this invention is to provide a print memberrestraining device in a serial matrix printer which is flexible andresiliently supported, and which can be variably moved to differentpositions in accordance with the desired home position of the printmember yet retaining its effectiveness.

The preceding and other objects are attained in accordance with thepractice of the present invention by providing a flexible, elongateelement adjacent the printing member when in the initial or homeposition. When the printing member is returned to the home position atthe end of each printing line, it engages the element which serves torestrain undulations and vibrations of the printing member created bythe fast return. The restraining element is supported at its two ends,one end being fixed adjacent the fixed end of the printing member andthe other end being movably secured along the printing line so as to bevariably settable at the left end of each printing line. The restrainingelement is approximately the same length as the printing member so as tohave a configuration similar thereto intermediate the two ends andconform approximately to the curvature of the printing member in thehome position. The restraining element has a vibration absorbingmaterial thereon which serves to dampen vibrational movement set: up inthe element by impact with the printing member. In order to accommodateall home positions of the printing member, auxiliary resilient means areincluded to be effective at only selected ones of the positions to whichthe restraint element can be set. The auxiliary resilient means providea change in the damping characteristics of the restraint element whichis necessary because of the changing vibrational characteristics in theprinting member at various home positions. The restraint element iscoated on its surface adjacent the printing member with a frictionreducing material so that the printing member is not subjected tosticking and undue wear. The restraint element, by being coextensivewith the printing member, is able to limit vibrational amplitudethroughout the length of the printing member.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings wherein:

FIGURE 1 is a plan view of a serial matrix printer showing the printingmember and arrangement of a restraining element therefor in accordancewith the principles of the invention; and

FIGURE 2 is a sectional view of the printing member and restrainingelement in conjunction with a vibration damping brush taken along theline 2-2 of FIG. 1.

Referring to FIG. 1, the serial matrix printer apparatus comprisesgenerally a stationary control mechanism 10 and a flexible print wireharness 11, including a matrix print head 12. The print head is securedto a band 14 which can be moved incrementally or continuously along ahorizontal supporting track 13 by any suitable mechanism such aselectrostatic clutches 15, 16. During serial printing, the print head isincremented from the left toward the right by energizing clutch 16 and,upon completion of a printing line, the print head is returned towardthe left by energizing clutch 15. At each print position to which theprint head is moved, the control mechanism is actuated by appropriateinput signals to simultaneously project selected print wires through theharness 11 and from the print head 12 to produce the character desired.The wire ends move an ink ribbon (not shown) against theplaten-supported document to be printed thus leaving an impression of acharacter on the document.

The print head movement is limited by stops 20, 21 and limit switches22, 23 which serve as auxiliary controls to terminate movement of theprint head at each end of travel. The stops and limit switches areadjustable to different line lengths as may be required by the formbeing printed.

Adjacent the home position of the print harness at the left limit oftravel, there is provided restraining element 25 which is secured to abracket 26 on adjustable stop 20. The restraining element is secured atits other end to fixed supports 27 and 36 on stationary controlmechanism 10. The flexible restraint element is preferably a thin,continuous strip formed of metal such as spring steel a few thousandthsof an inch in thickness. The strip is approximately the same length asthe print harness and is unsupported between its two ends so that it isthereby free to move horizontally. The restraint element has securedthereto on the outside, away from the print harness, a vibration dampingmaterial 28 such as foam polyurethane or other nonmetallic material. Inorder to minimize friction between the restraint element and the printharness, the element has bonded thereto on the inside, toward theharness, a friction reducing material 29 such as Teflon, a product ofthe E. I. du Pont de Nemours and Co., Inc. The layers of the laminatedrestraint member can be seen in FIG. 2.

At the end of each printing line (left to right serial printing), printwire harness 11 is returned to the left home position rapidly andsuddenly stopped at the desired position. Limit stop is positioned sothat the print wire harness contacts the restraint element substantiallyalong the entire length of the harness. The flexibility of the restraintelement allows it to conform to the curvature of the harness and thefoam backing on the element damps vibrations set up in the restraintelement. By proper positioning of the limit stop 20, harness 11including print head 12 can be accurately brought to the desiredposition by overtraveling a predetermined minimal distance andincrementing toward the right to the home position. It will be notedthat the restraint element is substantially the same length and heightas the print wire harness so that at the extreme left emergency stopposition both the harness and the elements are in substantially paralleladjacent planes. This position establishes the proper length of therestraint element.

One of the requirements of the printing apparatus is that the print headbe capable of starting from any print position as a home position. Thus,limit stop 20 is movable to the desired home position for the length ofprinting line required. Therefore, one end of the restraint element isalso movable to the required position. However, as the length of theprinting line is shortened (or a given character rate) the frequency ofreturn, or line rate, is higher thus changing the frequency of vibrationset up in print harness 11. This change in forcing frequency iscompensated, however, by the provision of an auxiliary resilient member30 which is secured to brackets 31 and 26 supported on limit stop 20.When the home position and limit stop 20 are in the approximate lefttwo-thirds of the printing line, resilient spring 30 contacts restraintelement 25 only at one point 32. However, when the restraint element andlimit stop 20 are moved further toward the right, for example, to theposition shown in phantom, the auxiliary member 30 contacts therestraint element at a second point 33. Note that the acute anglebetween the mounting surface of resilient spring 30 and restraintelement 25, at the pont of contact 32, decreases as limit stop 20 ismoved from left to right thus varying the amount and direction ofapplied spring force at this point in the desired manner. The auxiliarymember 3t thus provides decreasing stiffness at point 32, but adds asecond support point for the higher line rate operation of the printharness in order to reduce the changing amplitude of vibrationalundulations set up in the print harness and restraint element.

During the forward incrementing of the print wire harness at the time ofprinting, the sudden stopping and starting of the print head at theprint line creates a second mode of vibration at the character rate.This vibration is of varying amplitude dependent upon the frequency withwhich the incrementing occurs. Vibration due to forward incrementing isdamped by providing a light resistance element 34 constantly in contactwith the print wire harness during operation. The resistance element isa brushlike device made of plastic material, such as polyurethane, withbristles 35 in contact with the bottom edge of harness 11, and is shownmost clearly in FIG. 2. The plastic brush is also effective followingthe return sweep of the print harness for subduing minor vibrationalamplitudes.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a machine having an elongate printing member movable from anextended position to a retracted position, vibration control apparatuscomprising:

an elongate, flexible element in juxtaposition with said member when insaid retracted position and having a surface which is engaged by saidmember upon retraction; and

a damping material secured to said element for absorbing vibrationsoccurring therein.

2. In a printing machine having an elongate, flexible printing memberhaving one end fixed and the other end movable from an extended positionto a retracted position, said printing member being unsupported betweenits ends, vibration control apparatus comprising:

an elongate, flexible element in juxtaposition with said member when insaid retracted position and having a surface which is engaged bysubstantially said entire unsupported length of said member; and

a coating of flexible, vibration-absorbing material secured to saidelement adjacent said surface.

3. In a printing machine, the combination comprising:

a printing member having one end fixed and the other end movable along aprinting line between protracted and retracted positions and beingunsupported between its ends;

means for moving said member between said positions;

and

flexible means supported for impact by said member when moved to saidretracted position for limiting the amplitude of vibrations in saidmember created by the movement thereof.

4. Apparatus as described in claim 3 further comprising:

a coating of flexible nonmetallic material on said flexible means fordamping vibrations occurring therein.

5. In a printing machine, the combination comprising:

an elongate printing member having one end fixed and the other endmovable from a protracted to a retracted position and :being unsupportedbetween said ends;

means for retracting said member;

an elongate, flexible element of length substantially equal to theunsupported length of said member and supported at its ends for impactby said member when moved to said retracted position; and

means along said element for absorbing vibrations created in saidelement by said impact. 6. Apparatus as described in claim 5 furtherincluding resilient support means at one end of said element effectivefor absorbing the shock developed by said impact.

7. Apparatus as described in claim 5 further comprising a plurality offlexible bristles adjacent said member and engageable thereby during andfollowing said retraction for damping vibrations occurring in saidmember.

8. In a printing machine, the combination comprising: an elongateprinting member having one end fixed and the other end movable along aprinting line between a protracted position and variable retractedpositions;

means for moving said member to said retracted positions; elongate,flexible, impact receiving means supported adjacent said retractedpositions for impact by said member along its length when moved to saidretracted position, said impact receiving means being movable tocorrespond to said variable positions; and

vibration absorbing material on said impact receiving means for dampingvibrations developed therein by said impact.

9. Apparatus as described in claim 8 further comprising:

auxiliary support means operable when said impact receiving means isadjacent predetermined ones of said variable positions for providing aresilient sup- References Cited UNITED STATES PATENTS 2,129,065 9/1938Loop 197-1 2,720,164 10/1955 Braun et al 1971 X 2,785,627 3/1957 Johnson197-1 X 2,911,085 11/1959 Leathers 1971 3,236,351 2/1966 Fitch et al197-1 ROBERT E. PULFREY, Primary Examiner. E. S. BURR, AssistantExaminer.

1. IN A MACHINE HAVING AN ELONGATE PRINTING MEMBER MOVABLE FROM ANEXTENDED POSITION TO A RETRACTED POSITION, VIBRATION CONTROL APPARATUSCOMPRISING: AN ELONGATE, FLEXIBLE ELEMENT IN JUXTAPOSITION WITH SAIDMEMBER WHEN IN SAID RETRACTED POSITION AND HAVING A SURFACE WHICH ISENGAGED BY SAID MEMBER UPON RETRACTION; AND A DAMPING MATERIAL SECUREDTO SAID ELEMENT FOR ABSORBING VIBRATIONS OCCURRING THEREIN.